[Collins] FW: AN/VRC-24 UHF radio

Tue Jun 24 14:47:13 EDT 2014

Been too long since I worked on them (60's) so I would have to claim 
ignorance as Jim already had you check the relays and the voltages I would 
suspect in transmitting. As for the tubes well a 6442 is nos on ebay at the 
moment for 34.00 . Course nos is not new by any means. Also the 7554 tube is 
available but from what I saw on a quick search over 100.00.
Anyway I will let Jim continue as he seems very knowledgeable and has a 
manual by the sounds of it or good memory.

Let me know how you make out
Steve N4YZA

-----Original Message----- 
From: Marco
Sent: Tuesday, June 24, 2014 1:36 PM
To: collins at mailman.qth.net
Subject: [Collins] FW: AN/VRC-24 UHF radio

I've pushed reply... 73' Marco

From: marcocasagrande2407 at hotmail.com
To: antqradio at sbcglobal.net
Subject: RE: [Collins] AN/VRC-24 UHF radio
Date: Tue, 24 Jun 2014 19:34:18 +0200

Dear jim and Steve,Many thank's for Yr prompt replies:I've checked the K-101 
and carefully cleaned the long ball end contact of K-102 relays, the 20 ohm 
resistor so all the rf connectors and checked all low power tubes, including 
the three 6j4WA. All tubes exibit more of 140-150% of efficiency!! From mine 
old box 6AK5,2C51 ecc only 90-95.... ;-) As from tech serv manual, I've 
checked all tube sockets dc voltages so unworking status resistance (pulling 
connectors) and retouched the various oscillators and relative tracking 
filters obtaining two valuable RF voltages at V-101 tx mixer (about 6-8 V rf 
up to dc, of plate voltage and 0.8-0.9 RF Volt to the catode)During signal 
tracing (pulling the three 6J4) have fused the 7554 (aghh!!) the filament is 
in series/parallel to 6442 and its filament adapter caps was leaking.. but 
now waiting the spare part, i've mounted a 5876 with similar gain and output 
voltage at 7554 output (about 5 RF Volt to 6442 catode at 399.9 Mhz) but 
only 1 R
F Volt is measured to the 4x150 control grid with tube pulled and max 
retouching of various trimmers (C127-C141). Could be out of minimum C class 
drive RF voltage limits or... the 6442 is Out?I've tried to test the 6442 on 
the table at 160 vdc and -15 to -2V grid biasing but only 5 mA at -2V is 
been measured. UmmmhCiaoMarco

> Date: Tue, 24 Jun 2014 08:59:28 -0700
> From: antqradio at sbcglobal.net
> Subject: Re: [Collins] AN/VRC-24 UHF radio
> To: marcocasagrande2407 at hotmail.com
>
> Marco
> I am familiar with the other variations of this UHF radio and there are 
> many.  The VRC-24 was the first but I worked on later versions like the 
> GRA-53, GRA-54 and the TRC-68.  There is also the Navy version, the URC-9. 
> If RX seems to be working and TX isn't, then there are only two tubes and 
> associated circuits that  could be the problem.  V-102, V-103 and V-104 
> are used in both RX and TX.  V-105 is a 6442 and V-105 is the 4X150D, the 
> D indicates a 24 volt filament.  These two tubes are used in TX only.
>
> First, I would check K-101 and K-102 relay contacts.  These two relays do 
> the reconfiguration between RX and TX.  You should be able to clean the 
> relay contacts with alcohol and some paste board like a match book cover. 
> I would not use a file or any such rough material.  If you have a 
> burnishing tool, so much the better.  If you still don't have TX at this 
> point, I would suspect either the 6442 or the 4X150D or the B+ to these 
> two tubes also check the fuses on the front panel.
>
> Once you get an indication of RF out in TX, then let me know.  There is a 
> trick to limit the need for tab bending when tuning the RF and Power 
> Amplifier for max output.
> Jim
> --------------------------------------------
> On Tue, 6/24/14, Marco <marcocasagrande2407 at hotmail.com> wrote:
>
>  Subject: [Collins] AN/VRC-24 UHF radio
>  To: "collins at mailman.qth.net" <collins at mailman.qth.net>
>  Date: Tuesday, June 24, 2014, 8:51 AM
>
>  Hi guys, I'm a couple weeks that I'm
>  going crazy to run this UHF radio in tx mode: don't push
>  enought driving signal in the rf power amp. module (J104)
>  but seems" receiving ok (no calibrated sign gen.).I bought
>  this "anvil to very little money but since it is very well
>  built, have motor, step actuators relays and many gears so I
>  would like her to sing her song. Is there here any Collins
>  wizard who has some additional tricks respect to the service
>  infos contained in its liberated" manual
>  (TM-11-5820-222-35). Thanks and 73 'Marco IZ0MFI
>
>
>
>
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